Anthraquinone Indanthrones

The syntheses of three polycyclic anthraquinones, indanthrone (53), pyranthrone (55a) and flavanthrone (55b), are illustrated in Scheme 4.7. In spite of the structural complexity of the products, the syntheses of these types of compound are often quite straightforward, involving, for... 

Scheme 4.7 Syntheses of the polycyclic anthraquinones indanthrone (53), pyranthrone (55a) and flavanthrone f55b)...

A number of vat dyes developed originally for textile applications are suitable, after conversion into an appropriate pigmentary physical form, for use in many paint and plastics applications. Examples of these so-called vat pigments include the anthraquinones, Indanthrone Blue (215, C. I. Pigment Blue 60) and Flavanthrone Yellow (216, C. I. Pigment... 

In 1901, mercury cataly2ed a-sulfonation of anthraquinone was discovered, and this led to the development of the chemistry of a-substituted anthraquinone derivatives (a-amino, a-chloro, a-hydroxy, and a,a -dihydroxyanthraquinones). In the same year R. Bohn discovered indanthrone. Afterward flavanthrone, pyranthrone, and ben2anthrone, etc, were synthesi2ed, and anthraquinone vat dyes such as ben2oylaniinoanthraquinone, anthrimides, and anthrimidocarba2oles were also invented. These anthraquinone derivatives were widely used to dye cotton with excellent fastness, and formed the basis of the anthraquinone vat dye industry. 

Some anthraquinone dyes are employed as organic pigments (see Pigments, organic). Examples appear in Figure 1. Indanthrone blue (6) is an important automotive paint pigment as is Cl Pigment Red 177 (7), a bisanthraquinonyl. 

Fig. 1. Anthraquinone dyes used as organic pigments (4) = dibromoan than throne [4378-61-4] (Cl Pigment Red 168 Cl Vat Orange 3 Cl 5930G) (5) = an anthrapyrimidine [4216-01 -7] (Cl Pigment YeUow 108 Cl Vat YeUow 20 Cl 68420)-, (6) = indanthrone blue [81-77-6] (Cl Pigment Blue 60 Cl Vat Blue 4 ...

Indanthrones. Indanthrone blue (Cl Vat Blue 4) [81-77-6] (6) (Cl 69800) is the first invented anthraquinone vat dye, and has been extensively used as the most important vat dye for many decades because of its bright color as well as excellent affinity and fastness. These advantages are considered to be due to the stable stmcture attained by the intramolecular hydrogen bonding (145). 

Indigo is the most important vat dye, dating back to ancient times and produced on an industrial scale since 1880. To replace the indigo dyes, the indanthrone (21) class of dyes was developed. Indanthrone has superior characteristics as a vat dye and became a key material for further development of anthraquinoid vat dyes. There exist a variety of anthraquinone vat dyes differing in the chromophoric system. The color-structure relationship of vat dyes have been rationalized by the Pariser-Parr-Pople molecular orbital (PPP MO) method. Some examples of commercialized anthraquinoid vat dyes are shown in Scheme 6.14... 

Apart from some nonclassified pigments such as Indanthrone Blue (P.131.60), the anthraquinone pigments, which are structurally or synthetically derived from the anthraquinone molecule, can be divided into the following four groups of polycyclic pigments. 

Most pigments derived from vat dyes are structurally based on anthraquinone derivatives such as indanthrone, flavanthrone, pyranthrone, or dibromoan-thanthrone. There are other polycyclic pigments which may be used directly in the form in which they are manufactured. This includes derivatives of naphthalene and perylene tetracarboxylic acid, dioxazine (Carbazole Violet), and tetrachloro-thioindigo. Quinacridone pigments, which were first introduced in 1958, and recently DPP pigments have been added to the series. 

Other five-membered heterocycles such as thiophenes, thiazoles and oxazoles have been successfully annellated in the anthraquinone series. For example, the yellow dye (12) may be prepared from 2,6-diaminoanthraquinone by condensation with benzotrichloride and sulfur. Similarly, the six-membered heterocycles acridines, quinoneazines, pyrazines, acridones and pyrimidines are frequently incorporated (B-52MI11201). In fact, the best known of the anthraquinone vat dyes are indanthrone (13) and flavanthrone (14). The former anthraquinoneazine, a beautiful blue, which was the first such structure to be manufactured on a large scale, may be prepared by alkali fusion of 2-aminoanthraquinone at 220 °C (27MI11200). Treatment of 2-aminoanthraquinone in nitrobenzene with antimony pentachloride yields the yellow flavanthrone (14), the structure being confirmed by Scholl (07CB1691). Both indanthrone and flavanthrone and their derivatives have attracted considerable commercial attention. 

Pigment Blue 60 [81-77-6] 69800 indanthrone intermolecular condensation of 2-amino-anthraquinone in presence of a strong inoiganic base and oxidizing agent... 

On the basis of their chemical constitutions the anthraquinoid vat dyes may be classified in the following major groups acylaminoanthraquinones, anthraqui-noneazoles, anthrimides and other linked anthraquinones, anthrimidocarbazoles, phthaloylacridones, benzanthrone dyes, indanthrones, and other polycondensed ring systems. 

Other important anthraquinone vat dyes belong to the family known as indanthrones. Important examples of this structural type are C.I. Vat Blue 4 and Vat Blue 6. Vat Blue 4 is made by heating 1-amino or 2-aminoan-thraquinone at 220-230°C in a K0H/H20 mixture. The Vat Blue 6 synthesis is a much longer process that requires the synthesis of 2-chloro-3-aminoanthraquinone.57 The resultant amine is brominated and converted to the target dye via an Ullmann reaction. 

In 1901, Rend Bohn, head of the BASF alizarin laboratory, applied the indigo reaction conditions to 2-aminoanthraquinone (46) and discovered a blue colorant that he named indanthrone, from indigo and anthraquinone . He then obtained the same product more directly from 46. Later known as indanthrene blue RS (47), it was the first of the anthraquinone vat dyes, more correctly anthraquinonoid vat dyes, also known as indanthrene dyes (Scheme 18). With this innovation, three types of anthraquinone dyes became available mordant (such as alizarin), acid (Robert E. Schmidt, at Bayer, 1894) and vat. 

Chemists at the rival Bayer company established the structure Indanthrone consists of two anthraquinone units joined through a heterocyclic bridge containing two nitrogens. This enabled industrial research laboratories to discover anthraquinone-based intermediates for other vat dyes. In 1904, an assistant of Bohn synthesized benzanthrone (48), later an important intermediate in processes involving aminoanthraquinone-derived colorants72. 

A typical use of 61 is, by fusion with potassium hydroxide at high temperature, in the production of flavanthrone (67) (Scheme 15). Fusion of 61 with potassium hydroxide under milder conditions affords the important anthraquinone azines known as indanthrones (Travis Chapter 1). The main vat-dye reactions proceed via anthrimides, which are both dyes and intermediates, since they are readily converted into cyclic carbazole derivatives. For example, benzanthrones, such as 68 and 69, dibenzanthrones, isodibenzanthrones, and their derivatives and substitution products, are important in vat-dye manufacture. An example of their use is in the synthesis of Cl Vat Olive T (70) (Scheme 16). Benzanthrone acridones made from 1-aminoanthraquinones are important green dyes. Certain vat-dye reactions require high-boiling organic solvents. 

In 1901 a most important discovery was made by Bohn. He endeavoured to make. e anthraquinone analogue of Indigo by fusing the substituted glycine, derived from 2 amino-anthraquinone, (13), with caustic soda. A blue vat dye was obtained, but instead of the anticipated product it was proved to be Indanthrone, (14), or Indanthren Blue RS(C.I. vatblue4) ... 

There are a number of different reactions which can occur during the reduction of anthraquinone or indanthrone vat dyes. The indanthrones can be reduced at two carbonyl groups, which, in this particular case, is desir-... 

The compound 5) was converted into its sodium salt with the appropriate quantity of sodium hydroxide and this proved to be stable, soluble in water, substantive to cellulose, and capable of being oxidized, on the fibre, to Indigotin (Indigo Blue). The anthraquinone dyes react similarly, an example being solubilized Indanthrone, (36). 

Blue 6B. See Direct blue 1 Blue anthraquinone pigment. See Indanthrone Blue base. See Dianisidine Bluebonnet extract Blue bottle extract. See Cornflower (Centaurea cyanus) extract Blue chamomile flower oil. See Chamomile (Matricaria chamomilla) flower oil Blue chamomile oil. See Matricaria (Chamomilla recutita) oil... 

The reaction of chlorobenzene with phthalic anhydride to yield 2-chloro-anthraquinone, which is used as an intermediate in the production of indanthrone (see Chapter 11.3.2), was of great industrial importance for the early tar-based dyestuffs industry. Reaction of phthalic anhydride with quinaldine yields quino-phthalone, which is the basis of the quinoline yellow dyes. 

The closely related flavanthrones and indanthrones are heterocyclic anthraquinones, both of which were first synthesised by R. Bohn in 1901. They are also vat dyes, capable of reduction to a leuco form. 

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